I don't know if this is the right place for this question or if there is a better one, if so, please forgive me :)
I recently bought an Apple Watch and soon enough found out that WhatsApp does not support the Watch, which made me kind of sad. Since i'm a software developer, I had the idea of simply building and distributing such an app through the app store for the other watch owners that felt the same. After searching a little bit, I found some code that I could get working which interacts with web.whatsapp.com, but also stumbled upon this repository where the developer seems to have gotten into trouble with the WhatsApp Inc.
Since I am not experienced in any kind of law (especially not american), I wanted to ask whether it is allowed to build such an app (in general). Where the boundaries of that are, especially for making profit of it, like: In-App-Advertisment, Donations or other ways of making profit. Another interesting thought on profit was to make a website that acts as landing page, that has advertisment on it, what about that ?
As far as I know I am also not allowed to use the Trademark "WhatsApp", any name that is close to "WhatsApp" or their logo or a logo that is looks too similar to the WhatsApp Logo ?
I know that are many questions and it's probably super specific, but that's why I would be even more stoked if somebody could answer them! Thanks in advance!